The present invention relates to an intermediate for the preparation of N-(L-aspartyl)-N'-(2,2,5,5-tetramethylcyclopentanecarbonyl)-R-1,1-diaminoe thane (hereinafter referred to as "gem-sweetener") represented by the formula: ##STR3##
The gem-sweetener is a known compound which is disclosed in European patent application No. 128654A. The compound possesses a high degree of sweetness, without undesirable flavor notes and also possesses a high degree of stability in all types of aqueous systems and even upon cooking.
It is known that the compound is prepared by the steps shown in the following scheme. ##STR4##
This method involves dangerous reactions, that is, Grignard reaction and hydroboration, and boron hydride which is used in the step of hydroboration is very expensive. Further, the total yield is only about 8% which is very low.
As the result of studies on an industrially advantageous process for the preparation of gem-sweetener, it has been found that 2,2,5,5-tetramethylcyclopentane carboxylic acid which is an intermediate for the preparation of gem-sweetener can be prepared without the above-described disadvantages of the known methods.